Means for indicating and/or recording unknown quantities



July 29, 19411 M. J. .JoHNsoN 2,250,712 MEANS FOR INDICAI'ING AND/0RRECORDIG UNKNOWN QUANTITIES 4 Filed July 9, 1938 2 Sheets-Sheet 1 mwN Q:me.

July 29, 1941 M.' J. JoHNsoN 2,250,712l NEANs Fon INDIcM-m'f AND/onREcoRDme uNKNowN QUANTI'TIES l Fi1ed Ju1y 9. 1958 2 sheets-sheet 2 yi @yATTORNE Patented July 29, 1941 MEANS FOR INDICATING AND/ 0R RECORD- INGUNKNOWN QUANTITIES Manfred J. Johnson, Naugatuck, Conn., assignor ofone-half to The Lewis Engineering Company,

Naugatuck, Conn.

Application July 9, 1 938, Serial No. 218,295

8 Claims.

This invention relates to potentiometers, and, more particularly, to thecalibrating slide wire type of instrument for indicating and lrecordingthe value of some unknown quantity, such as temperature, by measuringvoltage in thermocouples set up and varying with said temperatures.

In the potentiometers previously proposed of the calibrating slide wiretype, the means for compensating for variations in the temperature ofthe cold Junction of the-thermocouple were usually made a part of theslide wire, and a, common battery was employed for supplying current tothe slide Wire as well as to the cold Junction compensating means. Thisprior construction made accurate compensation dicult for diierent typesof thermocouples, and presented a very.

serious diillculty when it was desired to change the scale range oi.'the instrument.

According to the present invention, the meansfor compensating forvariations inI` temperature of the cold end junction of the couplecomprises a resistance bridge energized from anunvarying but adjustablesource of E. M. F. separate from the E. M. F. source for supplying thecurrent to the slide wire circuit. The bridge, furthermore, is providedwith legs of positive temperature coeilicient of resistance and legs ofnegative temperature coeillcient of resistance such that a considerabledi'erence in unbalance is obtained per degreein'change of temperature,and, accordingly, to this system there is also a comparatively smallcurrent required of the battery energizing plished by a separate bridgebetween the thermocouple and the slide wire independent of theresistance of the circuit of the slide wire, so that the scale range ofthe instrument may be changed by merely removing and replacing thecalibrated resistances by like but quantitatively different resistances,so that the balancing e'ect of the connector circuit supplied to thecalibrat- A ing slide wire will be correspondingly changed. Furthermore,to facilitate the adjustment of the scale range of the instrument, theresistances are Wound on small plug-like coils having means for quickremoval and replacement in the measuring circuit. The resistancespreferably bear a denite ratio one to the other, so that fractionalscale changes if desired may also be had.

Other features and advantages will hereinafter appear.

In the accompanying drawings:

Figure 1 is a schematic view of the potentiometer of the presentinvention, dlagrammatically showing the circuits employed. f Fig. 2 is adiagrammatic view of a part of the circuits employed, showing a modifiedform of the invention.

Fig. 3 is a fragmentary front elevational-.view of the panel of theinstrument.

Fig. lisa similar view, showing a chart having a different range oftemperature indication. In the preferred embodiment of the/presentinvention, referring now to Fig.- 1"of the accompanying drawings, thebalancing device comprises agalvanometer I 0 including an armature thebridge, -and therefore this battery will remain serviceable and giveconstant and unvarying energy over long periods of use. As thecompensating bridge is independent of the resistance of the circuit ofthe slide wire, the temperature or millivolt rangeof the instrument,when calibrated as a millivoltmeter, may be, according tothe presentinvention, quickly and conveniently' changedby a user by means of aplurality of removable calibrated resistances that are adapted to beconnected into the measuring circuit.

In the preferred form of the present invention,

Il and a needle I2 having a normal center zero position, as shown in thefigure vreferred to, from which it may be moved to the right or leftwhen the galvanometer is acted uponpby an E. M. F.

. The galvanometer I0 is in a circuit adapted to be connected to one ormore thermocouples I3'.

The thermocouples I3 are connected by wiresy ,44 to certainapparatus, anunknown quantity,

the replaceable resistances are used for` the purpose of providing ameans for'convenientlyvarying the resistance between the terminals ofthe slide wire, 'as well as to vary the value of the vvoltage dropacross the slide wire circuit.

Accordingly, in the potentiometer of the present invention incontradistinction to those ofA the prior construction r having acalibrating coil.

and cold end compe ation 'across the ends of the slide wire, cold endcompensation is accom- 1n connection' with which'is to be'indicated andrecorded. Each thermocouple is placed in an apparatus in accordance withthe usual or any 1 known manner. When athermocouple or othercondition-responsive device, as a resistance thermometer or a manometer,is connected-tothe ilect in one direction or the ,other. To

galvan'omete'r, the, current f from the conditionresponsive device ormeanscontrolled thereby causes the needle i2 of the galvanometer todeindicate the unknown quantity which thus causes the needlev todeflect, the recording instruments, such as,` recording potentiometers,arelprovided with means for applying `a counter and 'known quantity tothe galvanometer to balance the quantity applied thereto by thecondition-responsive device, and since the amount of the quantity ofcounter effect is known in advance, the unknown quantity may beindicated or recorded by the amount oi.' known quantity ywhich it wasnecessary to apply to thefgalvanometer in. order to return the needle tozero position. y f

As herein shown, this counter quantity is derived from a source of E. M.F., usually in the form of a storage battery I6, and the effect of thesource of E.' M. F. on the galvanometer Ill-is controlled by apotentiometer slide wire Il,` the potential.

drop acrossvthe terminals I8, I9 of the slide wire I1 being regulated bymeans of a variable rheovstat until a predeterminedcurrent measured by amilliammeter 2l flows through the slide wire circuit.

In` the potentiometer of the present invention in contradistinction tothe potentiometers previously proposed having a calibrating coil of coldend compensation across the end of` the slide wire, compensation for4temperature variations of the cold junction of the thermocouple isaccom' e plished by a separate bridge 22 between the thermocouple andtheslide wire which is independent of thefreslstance ofthe circuit of theslide wire and is supplied current from asource ot M.. F. separate anddistinct from the source I8.

According to the present invention, the bridge circuit is energized tocarry predetermined adjusted values of current to accurately compensate`over a wide range for cold junctions of various types of couples, andsaid circuit'has a separate battery 23l connected to an adjustingrheostat 24, the current supplied being measured by the meter V25. 'I'hebattery 23 and rheostat 24`are connected v to make the legs29 ofA nickeland the legs 230i a copper nickel alloy suchl as canstantan. The

bridge circuit is adjustedto give the same voltage thermocouple perdegree change in temperature. That is, when the temperature of thebridge 22 and cold junction of the thermocouple changes,

the wires` 26, 21 of theplaced in an apparatus and responds to a cer--prises a known-removable resistance, and as shown is provided with aplurality of prongs 3| adapted to be inserted into suitable socketsdiametrically shown at 32. A second removable plug-like resistance coil33 is adapted to be connected across the ends of the slide wire Il bymeans' of contact prongs 34 insertable within suitable socketsdiametrically shown at 35 and .36, electrically connected respectivelyto the terminals I8 and I9 of the slide wire I'I.

The resistance 33 is normally used to shunt the slide wire in order thatthe saine will have a denite known resistance. The slide wire I1 is'engaged intermediate its ends by a shiftable contact 38 connected by awire 33 to one terminal of the galvanometer I0. 'I'he terminal I9 o! theslide wire I1 is4 connected by means of the compensating circuit to theone side of the thermocouple I3, the other side of the thermocouplebeing'connected by the Wire I4 to the other terminal of thegalvanometer.

Thus, when the condition-responsive.device is tain condition, the needleI2 of the galvanometer may deect either tothe right or to the left, andit may be returned to-zero position by shifting thecontact point 38relative to the slide wire II4 until a counter quantity is applied tothe galvanometer by the source of E. M. F.' I6. The resistance of theslide wire I1 being known and the positions of the contact 38 havingbeen calibrated, the condition oi the apparatus containing thethermocouple which is in circuit will also be known.

It should be noted that the various .positions of the shiftable contact38 of the slide wire may .change as the cold junction E. M. F. change ofthe the drop 'acrosssaid bridge between the wires 26,

21 will change in a manner to compensate for the change in E. M. F. ofthe cold junction due to said temperature change. Also, it has beenfound that, by providinga bridge having one pair of legs of negativetemperature coefcient of v resistance and the other pair .of legs ofpositive temperature coeiilcient of resistance, the difference inunbalance of the bridge per degree change of temperature is much greaterthan if the bridge'did not have negative coeilicient legs, and thecornpensation for .variations of temperature is accomplished with thebridge operating -on less-current from the battery,I and, therefore,said battery will give more uniform and accurate service and'will lastlonger in use.

To obviate theV necessity of changing the bridge when a different typeof thermocouple is ema marking device 42 may travel. Asdiagrammaticallyindicated in Fig. 1, this marking device v is carried bya pointer 42a. connected to a gear segment 43 in mesh with a gear v44carried by a shaft 45 carrying the variable contact ,38. The

disk 40 may be rotated by suitable clockwork mechanism so thatconditions referred to will be recorded graphically over a period oftime, portions of which are indicated by previously prepared lines onthe record sheet 4I In the previo ly proposed brated as amillivoltmeterfthe cold end lunction compensating means was made a partof the slide wire circuit, and it-was dimcult to change the -millivoltor scale range of the instrument yand generally necessitated the returnof the instrument to the maker when it was desired to sired scale range.It will be understood that as 'the cold end compensating means in theseprior constructions 'were made a part o f the slide wire circuit, thevresistance ofl the means employed .was not independent-of 'theresistance of the slide '-wire and any change in the resistance of theslide wire naturally affected the resistance of the compensating meanswhich would then not instrumentsl cali-` 'recalibrate the'same for somenew deinstrument by changing the value function properly and theinstrument became inaccurate. f In the instrument of the presentinvention,

as the resistance of the means for compensating for errors inmeasurements due .to variations in temperature of the col-d'end of thethermocouple v 'I3'is independent of the slide `wire circuit and isseparately' energized', the millivolt range of "the instrument, andconsequently the temperature range, may be'easily adjusted. As has lbeenpreviously explained, the resistance afforded by the coil 33 is normallyused to shunt the slide wire l1 in order that the sa-me will'have adenite known resistance, but, as

will now be explained, provides in addition ameans for adjusting themillivolt range of the instrument and consequently also the temperaturerange.v 'I'he changeable resistance afforded by the coil 33, as will beunderstood, provides a Vmeans for conveniently changing the resistancebetween the terminals of the slide wire I1, and consequently the rangeof temperature quantitative -indications controlled by the Calibratingslide wire. I

Accordingly, if it is desired to change the maximum range of theinstrument, it is merely necessary -to substitute a ,different chart 4|having the proper indicia, indicating increments of-temperature betweenthe predetermined limits.de sired and remove the' known 'resistanceacross the e'nds of the slide wire and substitute a quantitatively-diierent one .which would increase or decrease the range of theinstrument from zero to the. desired reading dependingon-the resistanceof the substituted coil. The coil 30, in cases where the maximum 'rangeonly of the instrument is to be changed, is merely a' short circuit coiland has no resistance wound on it.

be-seen from referring to the circuit diagram.

shown in Fig. 1, will occupy the position of a lumped resistance in theslide wire circuit, and will blanket ou-t the lower scale reading of theof the'voltage drop across the slide wire circuit.

Thecoils, as previously explained. comprise the proper known resistancewound thereon. The substitution of coil `marked No. l on which is woundresistance 33, as previously explained,

alters the resistance between the terminals of the slide wire andproportion-ally changes Ithe millivolt range of the instrument.

By way of example again, if a user of the instrument desires but afractional range of 1000 to 2000 degrees F., rather than the originalrange of zero to 2000 degrees F., he may substitute on disk 40, a newchart 4| having indicia indicating increments between the now desiredlimits an-d replace the coil marked No. 2 in Fig. 3 with that-marked-No. 2'of Fig. 4, which, a-s will be now understood, places adenite series resistance in the slidewlre circuit which alters the valueof the voltage drop across the same and the instrument is now calibratedfor the new range indicated bythe new chart.

Igt will be understood, however, that if the maximum limit of the scalerange is also to be changed, then it would be necessary to substi-.plug-like units provided with suitable prongs 1 adapted to be inserted.within the respective contact sockets .whereby the resistances" carriedY. thereby are made a part of 'the slide wire circuit. 'I'o 'facilitatethe manipulation of the coils during an adjustment of the scale range ofan instrument, the coils are, as shown by Figs. 3 and 4, convenientlydisposed on the instrument 'panel so that the same are readilyaccessible.

Each coil, as Ait isconnected4 into the circuit by ,a prong-and-socketconnector,` may be quickly and veasily removed and a new coilsubstituted l therefor without use of any tools,

If a user of the instrument, a fragmentary part of the panel of which isshown in Fig.- 3, should,

vfor example, desire to recalibrate the instrument so as to have.instead of the' scale range shown,

'a range `or zero to 2500 degrees F., it is merely necessary tolsubstitute for the chart 4| `a new chart bearing' .the properindicia-and remove the coils 3l and 33 and replace the. same with dii'--ferent coils which are intended to be furnished' by the manufacturer ofthe instrument having tute a, different calibrated resistance betweenthe terminals of the slide wire. y

According to the present invention, for reasons which will appear below,it is'preierable to rotate the disk 40 by a, synchronous motor 46-through a suitable train of gearing. To this end, the motor has a pinion41 meshing with a gear 48 o n a shaft 49 carrying a pinion 50 meshing.with a gear 5I ona second shaft 52 having a worm 53 engaging a wormwheel 54 connected to a shaft carrying the disk 40. Thev shaft 52 ismounted in suitable bearings 56.

^ In accordance with Ithe invention herein disclosed, ythe-Jpower foradjusting the slide wire contact 3'8 is lderived from the'motor46 whichoperates the recording disk 40 as pointed out above. As has -been.described hereinabove, the

moi-,M146 has a pinion .41 meshing witlthe gear, '49 on the shaft 49.Theshaft 49 has a pulley 51 carrying a belt 58 leading to a pulley 59 ona drive shaft 50, having loosely mounted thereon,'c`ombined gear andclutch members 6| and I(i2 and having between the members 6i and 82 aclutch member 63 splined' on Ithe shaft 60. The clutch member 53 has anannular -groove 64 operated by a forked arm 65 pivoted at 96 and theforked arm 65 andclutch 63 are held in neutral position between .themembers 6i and 52 by a spring 61. A

When -the clutch member 53 is moved to the right. as viewed inFig. 1, itengages Ithe member 'El which'meshes with a gear 68 on a shaft 69 having'a worm 10 engaging a worm wheel 1i connected to the shaft 45 carryingthe slide wire contact 38 and thus causes the slide wire contact' tomove in one direction.

when. however, `the clutch member 63 is -moved f y to the left. itengages the member 6 2 which I meshes with a reverse gear 12 meshingwithV av gearA 13 on the shaft 89 causingthe slide wirev contact 33 tobe moved in the reverse direction.

The shafts Bl and $9 and the reverse gear 12 .v

are mounted in suitable bearingsv 14. The upper end of the clutchshifter 65 forms an arma ture 15 for la pair of electromagnets 16 andT1'.

`and it is by meansof these electromagnets that the -constantly rotatingmotor is made operative to cause the slide wire to move in one directionor the other.

The movements of the slide wire in one direction or the 'other arecontrolled by the off-zero `movements of the galvanometer needle I2, andin accordance with the direction ofsuch ofi-zero movement. To this end,the galvanometer needie is provided with a contact 'I9 cooperating withcontacts 88 and 8| on a drum 82 carried by the shaft 49. The cylindricalsurface of the drum is made concave, and the degree of concavity-thereof correspond-s with an arc `drawn about the pivot pin of thegalvanometer needle I2. The con-tact 19 of the galvanometer needle 'I2is substantially tangential to the cylindrical spaced away from thesurface of .the drum and out of contacting position so that the needleis free to shift under the very feeble 'torque of the galvanometer.Means are provided for bringing the contact 19 into contacting positionduring each revolution of the shaft I9 which depresses the galvanometerneedle to bring the contact 1'9 into contacting position with the drumand to lock or -hold the galvanometer needle against turning.

Accordingly, to bring the con-tact 19 into contacting position, there isprovided a yoke 84 pivoted on a shaft 85 and having an arm- 86 includinga follower 81 engaging an eccentric cam 89 mounted on the shaft 49.During each revolution of the shaft I9, the yoke is allowed to fall anddepress the galvanometerneedle to bring the contact 19 into contactingposition with the drum 82 and to lock or hold the galvancmeter needleagainsLmI-,urning.V The locking is effected by reason of an anvil 89located under the yoke 84 and between which and the yoke the needle I2is locked when the yoke is depressed.

The contacts 88 and 8| are electrically connected together andthe-directional control of the device is aected by contacts 98 and 9|lying on the anvil 89. These contacts 98 and 9| are separated byinsulation92.

Current for controlling the electromagnets 16 and 11 may be'suppliedfrom any suitable source,

jas, for 44exam-filma battery 93, and is-led therefrom .by a wire 94 toa brush 99 engaging a coll lector ring 99 in permanent electricalconnection wlththe contacts 88 and 8|: From the other 19 into contactingrelation with the drum. If

the needle I2 has ybeen deflected toward the left, as shown in Fig. 1,the contact 19 will be brought into engagement with the contact 88 andtheneedle itself will be brought into engagement with the directionalcontact 98. This will close the circuit through the-battery 93 and theelectromlagnet 16, thereby causing the amature 1l to move the clutchmember |53v in-to engagement with the member 8| which, as will beunderstood, causes movement of theslide Wire counterclockwise. Theextent of movement of the slide wire contact .38 will, of course, dependupon the width of the contact 88 at the point at which the nee- -dlecontact 19 engages the same. If the needle I2 is .deected toward theright, as shown in Fig. 1, the circuit will be closed between the drumcontact l8| and the anvil contact 9|, thus causing the electromagnet" tobe energized and causing the slide wire -to be moved clockwise throughthe shaft 89, reverse gear 12, clutch member 83 and armature 15. Thecontacts 88, 8| and the slide wire and mechanical parts operating thesame may be so arranged .that in a single adjusting operation the`system may be balanced, `thereby avoiding step-by-step adjustments ofthe slide wire to bring 'the circuit unit into balance and indicate .theunknown quantity.

In the form of my invention shown in Fig. 2, which is a diagrammaticview of the circuits employed when a` standard cell |84 is used in placeof the milliammeter 2|, thecounter quantity is derived from a source 'ofE. M. F., usually in the form ofa storage battery |85 land the effect of'the source of E. M. F. on the galvanometer, not shown. is controlled bythe potentiometer slide 'wire |81, and, as in the preferred form of theinvention, the potential drop across the terminals |88, |89 is regulatedby an auxiliary resistance II8 inV comparison with the standard cell |84by means of a galvanome'ter Il I.

tered.- v

side of the battery, current ows through wire 91 to. branches 98 and -98to the electromagnets' 19 and 11.. The electromagnets 18, 11 areconnected respectivelyby wires |88 and IIII- to theV contacts 98 and 9|.

, The movements of the slide wire contact 38 are controlledquantitatively by contacts 88 andj 8| von the drum 82,' andlaccordlngly,these contacts'are wider o n their outsideends and taperoil' toward the center of the drum.' that is, the

cases, at'the zero position theldrurn-` carries an g ,anmuus In: of'insluiting material against which 'the contact 19 may be pressed in thezero position ofthe needle I2. If desired, the nonconduct- When theapparatus is I2 lis depressed periodically to zero'positio'n' of theneedle I2.'V The remaining I surface of .the drumis made soasnotto con-'stitute a contactby being'cxt away, and, in such In the form of theinvention just described, a greater degree of 'accuracy is permittedthan in the preferred form of the invention, but is not practical inapplications where extremely low temperatures and excessive vibration isencoun- Variations titles within such limi-ts; a potentiometeigcircuitincluding a 'slide wire having a 'movable part controlling the positionof said member to indicate quantities according to a predetermined.plan.: a thermoelectric ccupleincluded in a circuit therefor;,separately `energized bridge 'means in said thermoelectrlccouplecircuit for automatlcally compensating for errors iny measurementsdue to changes in temperature of the cold end of said' couple, theresistancefof which is independent'of the resistance 'ofthe slide wire:

in operation, the needle `and, means for determining the value of thevolt- ,age drop across the slide wire circuit, said means. jbeingremovable from said circuit for capiscement ,bya like but quantitativelydifferent means to change thevalue of the voltage drop across the slidewire circuit so as' to raise or lower the the contact lower limi-t ofreading indicated bythe member merchant and modifications -maybemade Iwithin the scope of this invention'and portions 'of the improvements maybe used without others.

cooperatingwi-th the scale-iii accordance with a different predeterminedplan.

2. In an indicating instrument having a member adapted to be variouslypositioned over a scale having readings within predetermined limits anddivided into increments indicating quantities within such limits apotentiometer circuit including a source of current and a slide wirehaving a movable part controlling the position of said member toindicate quantities according to a predetermined plan; a thermoelectriccouple included in a circuit vtherefor connected to said potentiometercircuit; means in said thermoelectric couple circuit for automaticallycompensa-ting for errors in measurements due'to changes in temperatureof the cold end of said cou-ple, said means includinga bridge energizedfrom a source vof current separate from the one first mentioned, theresistance of which bridge is independent of the slide wire; and meansinterconnecting the slide wire proper and the cold end compensationmea-ns for ldetermining the value of the voltage drop across the slidewire circuit, said means being removable from said `circuit forreplacement by a like but .quantitatively diieren-t means to vary thevalue of the f voltage drop across the slide wire circuit so as urementsdue to changes in temperature of the cold end of said thermoelectriccouple including a bridge resistance in the couple circuit independentof the resistance of the slide wire; means for connecting said couplecircuit tothe potentiometer circuit, said means including a knownresistance and adapted to determine the value of the voltage drop acrossthe slide wire circuit,

and being manually removable for substitution of a similar butquantitatively different resistance whereby the lower limi-t ofmeasurement of.

the instrument may be raised or lowered `in accordance with the lowerlimit on the scale chosen for use in the instrument.

4. In a temperature measuring instrument of.l

the type described, a calibrating slide wire;` a

thermoelectric cou-ple incmded in a circuitncon-l nected to said slidewire; means for automatical- 'ly compensating for errors in measurementsdue to changes in temperature of the cold end of the thermoelectrlccouple including a separately energized bridgev having a resistancewhich is independent of .the resistance of the slide wire; and

'means for adjusting the millivol-t range of the instrument whereby thescale of the instrument may be correspondingly adjusted, said meansincluding manually removable resistance means replaceable' with like.but quantitatively different resistance means, at least some of saidmeans being series` connected in the slide wire circuit `forvchangingthe resistance of said circuit, the others being shunted across theterminals of the slide wire. proper for changing the resistance betweensaid terminals. i

5. In a temperature measuring instrument` of thermoelectric couple;means for automatically compensating for errors in measurements due tochanges in temperature of the cold end of the thermoelectric coupleincluding a separately energized bridge, the resistance of which isindependent of the resistance of the slide Wire; .and means foradjusting the millivolt range of Ithe instrument whereby the scale ofthe instrument may be correspondingly adjusted, said means including amanually removable resistance comprising a plug-like coil adapted to beconnected across the terminalsof the slide wire for altering theresistance between the same and being replaceable by a like butquantitatively diii'erent resistance.

` 6. An indicating instrument comprising a. deiiector operating on thezero principle; means, including a thermoelectric couple, for causing anunknown quantity Ito act on the deiiector; means, including a balancingcircuit, for applying a count-er quantity to the deflector; means forautomatically compensating for `modifications in said unknownV quantitydue to changes-in temperature of the cold end of the'thermoelectriccouple including a separately energized bridge, the resi-stance of whichis independent of the resistance of said balancing circuit; and meansfor adjusting the scale range of the instrument including means forvarying the effect'of the counter quantity, Said means comprising aplurality of calibrated resistances manually replaceunknown quantity toact on the deflector; means, l

including a calibrating slide wire, for applying a counter quantity tothe deiiector; means for automatically compensating for errors in.measuremen-t-s due to changes in ltemperature of the cold end of the-thenmoelectriccouple including. a separately energized bridge, theresistance of which is independent of theresistance of the slide wire;and means for adjusting the scale vrange of the instrument includingmeans f or varying the effect of the counter quantity, said meanscomprising a plurality of calibrated resistances replaceable by like butquantitatively diierent resistances, at lea-st one of said resistancescomprising a shunt resistance across thek 8. indicatingr instrum" entcomprlsillfa deilector operating on the zero principle; a pointeradapted to be variously positioned over a scale having readings`withinpredeiermined limits and divided into increments indicatingquantities' within such limits; -circuit means, including athermoelectric couple, for causing an unknown 'quantity to act onthedeilector; circuitmeans.-

.including a caiibrating' slide wire and a 'movable contact, forapplying a 'counter quantity to said deflectior, said contactcontrolling the position of the pointer relative to said scale toindicate the counter quantity according to a lpredetermined' plan; meansfor automatically compensating for errors in measurements due to changesin Itemperature of the cold end of the thermoelectric couple including aseparately energized 4bridge'.4

the type described, a Calibrating slide wire; a

y terminals. said resistances being removable for substitution ofsimilar but quantitatively different resistances whereby the limits ofquantitative indications controlled by the contact may be changed inaccordance with -a scale having readings within different predeterminedlimits.

MANFRED J. JOHNSON.

